248 THE SALAMANDER 



There is, however, a Vena communicans forming an anastomosis 

 between the Vena craniaHs pro-otica of either side. It passes between 

 the roots of nerve V, dorsal to the pituitary body, and receives a pair 

 of tributaries therefrom. 



The -pituitary veins (v.pit.), one on either side, arise from the pos- 

 terior edge of the pituitary body. 



At the posterior corners of the plexus covering the fourth ventricle 

 the network collects into a single vessel which also receives one or 

 two basal veins from the ventral side, and then passes out of the 

 cranial cavity together with the combined nerves IX and X. This 

 is the sinus jugularis of Rex, but to avoid confusion with the jugular 

 vein it may be called Vena cranialis post-otica (v.cr.po-ot.). It enters 

 the occipital vein (q.v.) and is equivalent to the Vena cerebralis pos- 

 terior of van Gelderen. In Triton it forms the principal venous exit, 

 the Vena cranialis pro-otica being quite small (Rex). 



The region of the medulla behind this point and the anterior 

 section of the spinal cord are surrounded by an irregular, wide- 

 meshed, venous network which again collects into a vessel leaving 

 the neural canal through a foramen in the first vertebra, the Vena 

 post-occipitalis (v.po-oc.) (Gaupp, Frog). 



Almost immediately behind this point a definite dorsal longitu- 

 dinal vein maybe traced right down the spinal cord. This is the Vena 

 spinalis superior (Gaupp), and collects the blood from the Arteria 

 spinalis centralis. It is connected with the Venae post-occipitales by 

 a fairly definite branch. 



Summary of Vessels of the Brain. 



It will have been noticed that the main arteries are almost entirely 

 confined to the ventral surface, while the larger venous vessels occur 

 dorsally. Further, the arteries are more closely applied to the neural 

 tissue than are the veins. The connexions between the arteries and the 

 veins within the substance of the brain have been shown by Scholb to 

 consist of simple loops, which may be spirally twisted but never 

 branched. 



The vascular plexuses fall under three distinct heads : 



(i) Those to which the blood is carried by arteries and drained 

 by veins. These are the internal plexuses, viz. the lateral plexuses of 

 the first ventricle^ and the superior and inferior median plexuses of the 

 diencephalon. 



(ii) Those to which the blood is carried by both arteries and 

 veins, viz. the nodus chorioideus and the plexus covering the fourth 

 ventricle. 



